Snowmobile construction

ABSTRACT

A snowmobile design, including a modular front suspension system and a stabilizer assembly, a lightweight frame structure and a drive train that reduces the center of gravity of the snowmobile. The modular front suspension system for a snowmobile that is substantially self-contained and self-supporting. The present modular front suspension system is assembled around a primary support structure, such as an extrusion or other structural member. The primary support structure can be easily attached to, or detached from, the snowmobile frame. The modularity of the present suspension system decreases assembly costs. A stabilizer assembly extends through the center opening and is mechanically coupled to the ski spindle housings.  
     The chassis for a snowmobile includes a plurality of front structural members defining a motor compartment. A pair of independent, rear structural members are rigidly connected to the front structural members and extend rearwardly from the motor compartment on opposite sides of an endless belt channel. A protective shell extends between the pair of rear structural members and over the endless belt channel. The protective shell comprises a light-weight, resin based material that transfers substantially no loads between the pair of rear structural members. The snowmobile chassis further includes a rear suspension system extending between the pair of rear structural members. The rear suspension system transfers substantially all loads between the pair of rear structural members.

[0001] The present application claims the benefit of prior filed U.S. provisional application No. 60/114,330 entitled Modular Front Suspension System and Stabilizer Assembly for a Snowmobile, filed Dec. 31, 1998, and U.S. provisional application No. 60/130,000 entitled Snowmobile Construction, filed Apr. 19, 1999.

FIELD OF THE INVENTION

[0002] This invention is directed to various innovations in snowmobile design, including a modular front suspension system and a stabilizer assembly, a lightweight frame structure and a drive train that reduces the center of gravity of the snowmobile.

BACKGROUND OF THE INVENTION

[0003] Snowmobile design has incrementally moved towards more powerful motors, with a resulting increase in the weight of the machines due to the larger motor and corresponding support structure. Frequently, increased weight results in a higher center of gravity of the snowmobile. Increased weight and increased center of gravity can have a detrimental affect on the ride quality and handling characteristics of the snowmobile.

[0004] Handling, cornering and ride quality are largely dependent upon the front suspension system of the snowmobile. It is common practice to suspend the skis of a snowmobile independently by means of respective strut type suspensions. It is desirable to provide some form of stabilizer or sway bar arrangement interconnecting the front skis to reduce the amount of leaning that occurs during cornering of the snowmobile. Due to the rough and sometimes uncertain terrain over which snowmobiles are ridden, it is desirable that the stabilizer arrangement be positioned so that it will be protected if unexpected objects are encountered, such as disclosed in U.S. Pat. No. 4,690,234 (Takada).

[0005] U.S. Pat. No. 4,489,954 discloses an anti-roll mechanism that includes a torsion bar supported by the body that is connected to the skis for torsion loading upon independent movement of the skis relative to the body. The connection between each of the skis and the torsion bar is such that the torsion bar is loaded by the pivotal movement of the skis about their steering axes for providing a self-centering force on the skis.

[0006] U.S. Pat. No. 4,671,521 (Talbot, et al) discloses a snowmobile ski suspension including upper and lower transverse suspension arms vertically spaced and each having an outboard end articulated to a ski spindle and an inboard end articulated to a fixed mounting on the frame of the snowmobile. The upper and lower transverse suspension arms define a parallelogram linkage for guiding the spindle to move generally vertically with respect to the snowmobile.

[0007] U.S. Pat. No. 5,029,664 (Zuwalski) discloses a suspension system with a geometry that includes upper and lower suspension linkages of predetermined lengths in cooperation with a spindle of a predetermined length for eliminating lateral movement of the skis during suspension travel. The respective linkages and spindles are interconnected by ball joints at predetermined locations in such a manner that during deflection of the suspension system, a ski attached to the lower end of the spindle moves substantially in a line parallel to a vertical plane which contains the longitudinal axis of the snowmobile.

[0008] What is needed is a snowmobile design that provides a high power-to-weigh ratio while maintaining optimum handling characteristics and ride quality.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention is directed to various innovations in snowmobile design. In one embodiment, the snowmobile includes a modular front suspension system and a stabilizer assembly. In another embodiment, the frame structure includes a light weight frame structure. In yet another embodiment, the snowmobile includes a drive train that reduces the center of gravity. Finally, all of these features are combined on a single snowmobile.

[0010] The present invention is directed to a modular front suspension system for a snowmobile that is substantially self-contained and self-supporting. The present modular front suspension system is assembled around a primary support structure, such as an extrusion or other structural member. The primary support structure can be easily attached to, or detached from, the snowmobile frame. The modularity of the present suspension system decreases assembly costs.

[0011] The front suspension system of a snowmobile is typically assembled directly to the frame of the snowmobile. The present modular front suspension system can be assembled independently of the snowmobile and conveniently transported or stored for later use. The self-contained, self-supporting nature of the present suspension system allows for lower cost assembly, machine handling and automated testing.

[0012] Repairs on conventional snowmobile suspension systems are often accomplished by replacing individual components. End-users, however, typically lack the proper equipment to determine whether the front suspension system is operating properly. The present front suspension system can be easily removed by the user and returned to the manufacturer for factory repair. A temporary or permanent replacement suspension systems can also be sent to the customer for easy installation.

[0013] Additionally, a standardized primary support structure can be utilized so that a variety of suspension systems with different features can be easily substituted on the snowmobile by the manufacture, the dealer or the end-user. Since the front suspension system is less expensive than the entire snowmobile, the manufacturer/dealer can offer a variety of options with lower inventory costs. The end-user may also purchase multiple front suspension systems for a single snowmobile. For example, the end-user may have one front suspension system for racing and another for touring.

[0014] In one embodiment, the modular front suspension system includes a primary support structure having first and second ends, a center opening and at least one mounting surface attachable to the chassis. A pair of upper control arms are pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively. A pair of lower control arms are pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively. A pair of ski spindle housings are pivotally connected to distal ends of the upper and lower control arms, respectively. The ski spindle housings are connectable to the steerable skis. A stabilizer assembly is mechanically coupled to the ski spindle housings. In one embodiment, the stabilizer assembly extends through the center opening and is mechanically coupled to the ski spindle housings.

[0015] In another embodiment, the modular front suspension system includes a primary support structure having first and second ends, a center opening and at least one mounting surface attachable to the chassis. A pair of upper control arms are pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively. A pair of lower control arms are pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively. A pair of ski spindle housings are pivotally connected to distal ends of the upper and lower control arms, respectively. The ski spindle housings are connectable to the steerable skis. A pair of shock mounts are pivotally attached to one of the upper control arm or primary support structure, respectively. A pair of shock absorber are attached to the shock mounts and the spindle housings, respectively.

[0016] The present invention is also directed to a stabilizer assembly for use in a front suspension system on a snowmobile. The present stabilizer assembly may be used with or without the present modular front suspension system.

[0017] To provide flat cornering on smooth terrain, the front suspension system initially provides stiff resistance to ski displacement. In the event that rough terrain is encountered, subsequent ski displacement is preferably less stiff. That is, the force per unit displacement decreases with greater displacement. For example, the front suspension system provides stiff resistance to ski displacement during high-speed turns. If bumps are encountered during the turn, the front stabilizer system provides less resistance to ski displacement as compared to its initial movement. In one embodiment, the force per unit displacement curve is a step function, with greater force per unit displacement required during initial displacement and less additional force per unit displacement for subsequent displacement.

[0018] In one embodiment, the present stabilizer system includes first and second stabilizer brackets attached to the control arms, respectively. A rocker arm having first and second ends is pivotally mounted to the snowmobile. A first stabilizer member assembly is pivotally connected to the first stabilizer bracket and the first end of the rocker arm. A second stabilizer member assembly is pivotally connected to the second stabilizer bracket and the second end of the rocker arm. The stabilizer system transfers load from one side of the snowmobile to another. That is, spring force from one side of the snowmobile is transferred to the side experiencing the greatest ski displacement. In one embodiment, the actual spring rate on the stabilizer member assemblies can be different from ski to ski.

[0019] In one embodiment, the stabilizer member assembly includes an extendable rod assembly having a maximum extension and a spring cap fixed thereto. A sleeve is slidably engaged with the extendable rod assembly adjacent to the first stabilizer bracket. A spring is arranged around the extendable rod assembly and interposed between the spring cap and the sleeve. In one embodiment, an adjustment mechanism is provided for sliding the sleeve along the extendable rod assembly to apply a bias of the spring. The extendable rod assembly is typically a telescoping structure. The stabilizer member assemblies are typically in a fully extended or topped-out configuration in a level or horizontal resting state.

[0020] The stabilizer member assemblies can be configured to provide a preload in the horizontal resting state such that initial upward displacement of one of the skis is resisted by a first force, and subsequent upward displacement of that ski is resisted by the addition of a second force proportionally less than the first force. In another embodiment, the first stabilizer member assembly is a double-acting spring assembly and the second stabilizer members assembly comprises a rigid shaft.

[0021] The present modular front suspension system and the present stabilizer assembly have application in other vehicles, such as automobiles, trucks and all-terrain vehicles.

[0022] The present invention is also directed to a chassis for a snowmobile having an endless belt drive system. The chassis includes a plurality of front structural members defining a motor compartment. Front suspension system mounting locations are positioned on distal ends of two or more of the front structural members. A pair of independent, rear structural members are rigidly connected to the front structural members and extend rearwardly from the motor compartment on opposite sides of an endless belt channel. A protective shell extends between the pair of rear structural members and over the endless belt channel. In one embodiment, the protective shell comprises a lightweight, resin based material that transfers substantially no loads between the pair of rear structural members. The snowmobile chassis further includes a rear suspension system extending between the pair of rear structural members. The rear suspension system transfers substantially all loads between the pair of rear structural members.

[0023] In one embodiment, the snowmobile chassis includes a motor located in the motor compartment. The motor has at least one carburetor positioned on a first side of the motor adjacent to the front suspension system mounting locations and an exhaust port positioned on a second side of the motor.

[0024] The present invention is also directed to a snowmobile chassis having a motor compartment and an endless belt channel. A motor is located in the motor compartment. The motor has at least one carburetor positioned on a first side of the motor adjacent to a front suspension system and an exhaust port positioned on a second side of the motor. The motor has a drive clutch. A driven pulley is located on a gearbox that is located adjacent to the endless belt channel. An endless belt drive shaft is located in the endless belt channel and mechanically coupled directly to the gearbox. A drive belt mechanically couples the drive clutch to the driven pulley. A torque arm connects the driven pulley to the snowmobile chassis.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0025]FIG. 1 is a perspective view of a modular suspension system in accordance with the present invention.

[0026]FIG. 2 is a front view of a portion of the suspension system of FIG. 1.

[0027]FIG. 3 is a perspective view of a portion of a front suspension system in accordance with the present invention with the support structure removed.

[0028]FIG. 4 is an exploded view of a stabilizer member assembly in accordance with the present invention.

[0029]FIG. 4A illustrates an alternate stabilizer member assembly in accordance with the present invention.

[0030]FIG. 5 is a perspective view of a stabilizer system in accordance with the present invention.

[0031]FIG. 6 is a top view of the stabilizer system of FIG. 5.

[0032]FIG. 7 is a rear view of the stabilizer system of FIG. 5.

[0033]FIG. 8 is a perspective view of the present front suspension assembly mounted to a snowmobile frame.

[0034]FIG. 9 is a side view of a primary support structure in accordance with the present invention mounted to a snowmobile chassis.

[0035]FIG. 10 is a side perspective view of a snowmobile chassis in accordance with the present invention.

[0036]FIG. 11 is a front perspective view of a snowmobile chassis of FIG. 10.

[0037]FIG. 12 is a rear perspective view of a snowmobile chassis of FIG. 10.

[0038]FIG. 13 is a side view of a snowmobile motor and drive train in accordance with the present invention.

[0039]FIG. 14 is a top view of a snowmobile motor and drive train of FIG. 13.

[0040]FIG. 15 is a perspective view of a torque arm in accordance with the present invention.

[0041]FIG. 16 is an exploded view of a snowmobile gearbox in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] FIGS. 1-2 illustrate various aspects of a modular front suspension system 20 in accordance with the present invention. The various components of the modular front suspension system 20 are built around and attached to a primary support structure 22. In the illustrated embodiments, the primary support structure 22 comprises a hollow metal extrusion, preferably constructed from an aluminum alloy. In an alternate embodiment, the primary support structure 22 may be an I-beam, a solid member, a welded member, a cast member, a hollow member containing reinforcing webs, or a variety of other structures. Steering brackets 24 a, 24 b are attached to the primary support structure 22 for receiving a steering linkage mechanism (not shown).

[0043] Various mounting holes 23 are located on the primary support structure 22 for attachment to the snowmobile frame 200 (see FIGS. 8 and 9). The primary support structure 22 defines a center opening 72. Stabilizer assembly 74 is located in the center opening 72 (see also FIG. 9). Since the modular front suspension assembly is generally symmetrical, corresponding components are generally referred to herein with the suffix “a” or “b”, while these components may also be referred to generically without the suffix.

[0044] The modular front suspension system 20 includes upper control arms 28 a, 28 b pivotally mounted to the primary support structure 22 at upper control arm axes 30 a, 30 b. Lower control arms 32 a, 32 b are pivotally mounted to the primary support structure 22 at lower control arm axes 34 a, 34 b. In the illustrated embodiment, the upper control arm axes 30 a, 30 b are located above the lower control arm axes 34 a, 34 b, with respect to the front suspension system 20 being mounted to a snowmobile frame (see FIG. 8). Distal ends of the upper and lower control arms 28 a, 32 a, 28 b, 32 b are pivotally attached to spindle housings 36 a, 36 b at axes 40 a, 42 a, 40 b, 42 b, respectively. The spindle housings 36 a, 36 b includes openings 38 a, 38 b for receiving a ski spindle and ski (not shown).

[0045] Shock mounts 50 a, 50 b are pivotally attached to either the primary support structure 22 or the upper control arms axes 30 a, 30 b. In the illustrated embodiment, the shock mounts 50 a, 50 b are mounted to the primary support structure 22 along the upper control arm axes 30 a, 30 b. The shock mounts 50 a, 50 b includes a pair of holes defining axes 54 a, 54 b for receiving a shock absorber assembly 70 (see also FIG. 8).

[0046] Lower shock mounts 56 a, 56 b are rigidly attached to the respective spindle housings 36 a, 36 b. In an alternate embodiment, the lower shock mounts 56 a, 56 b can be attached to the lower control arms 32 a, 32 b, respectively. The upper control arms 28 a, 28 b include shock absorber openings 60 a, 60 b. The lower control arms 32 a, 32 b include shock absorber openings 62 a, 62 b. The shock absorber openings 60, 62 permit a shock absorbers 70 a, 70 b (see FIGS. 3 and 8) to be pivotally mounted to the axes 54 a, 54 b of the shock mounts 50 a, 50 b and axes 58 a, 58 b of the lower shock mounts 56 a, 56 b. As best seen in FIG. 2, lower portion of the shock mounts 50 a, 50 b are pivotally connected to the lower control arms 32 a, 32 b by links 69 a, 69 b. In another embodiment, the shock mounts 50 a, 50 b may be attached directly to the primary Support structure 22 or the vehicle chassis 240.

[0047] The stabilizer assembly 74 includes a rocker arm 76 pivotally mounted within the primary support structure 22 to rotate around an axis 78. First and second ends 80, 82 of the rocker arm 76 are pivotally attached to respective stabilizer member assemblies 84 a, 84 b. The stabilizer member assemblies 84 a, 84 b are pivotally attached to the lower control arms 32 a, 32 b by a pair of stabilizer brackets 88 a, 88 b (see FIG. 5). In an alternate embodiment, the stabilizer brackets 88 a, 88 b are pivotally attached to the upper control arms 28 a, 28 b or the shock mounts 50 a, 50 b.

[0048]FIG. 3 is a perspective view of one side of the present modular front suspension system 20 and a portion of the stabilizer assembly 74 with the primary support structure 22 removed. Shock absorber 70 a extends through the opening 60 a, 62 a in the upper and lower control arms 28 a, 32 a. In the illustrated embodiment, the shock absorber assembly 70 a includes a shock absorber 71 a surrounded by a spring 73 a, although other shock absorber or spring assemblies are possible.

[0049]FIG. 4 is an exploded view of the stabilizer member assemblies 84 a, 84 b in accordance with the present invention. Control arm mounting portion 90 includes a slot 92 for receiving a sliding nut 94 Rod 96 engages with the sliding nut 94. The sliding nut 94 permits the rod 96 to telescope or extend relative to the control arm-mounting portion 90 along the full length of the slot 92. The stabilizer member assemblies 84 a, 84 b top-out or bottom-out when the sliding nut 94 is at one end of the slot 92 or the other. Sleeve 98 slidably engages with outer surface 100 of the control arm-mounting portion 90. A bearing 102 is provided to facilitate pivotal engagement with the stabilizer brackets 88 a, 88 b (see FIG. 5). Retaining ring 104 holds the bearing 102 in opening 106 on the control arm-mounting portion 90.

[0050] Rocker arm mounting portion 108 also includes a bearing 110 to facilitate pivotal engagement with the rocker arm 76. Distal end of the shaft 112 includes a sleeve 114 and a spring cap 116 rigidly mounted thereto. Surface 118 of the spring cap 116 engages with surface 120 of spring 122. The opposite surface 124 of the spring 122 engages with surface 126 of the sleeve 98.

[0051] Stabilizer preload adjustment screw 128 is provided in the control arm-mounting portion 90 for sliding the sleeve 98 towards the spring 122. As will be discussed in detail below, the preload adjustment screw 128 permits the spring 122 to be preloaded to a desired level within the stabilizer member assemblies 84 a, 84 b.

[0052]FIG. 4A illustrates a double-acting spring assembly suitable for use as an alternate stabilizer member assembly 410 in accordance with the present invention. Control arm mounting portion 412 is attached to a sliding rod 414 that extends through a fixed divider 416 that is attached to a housing 418. A sliding retainer 420 that slides within the housing 418 is attached to the other end of the rod 414. A first spring 422 wraps around the rod 414 and is interposed between the sliding retainer 420 and the fixed divider 416. A second spring 424 wrap around the rod 414 and is interposed between the fixed divider 416 and an adjustable spring cap 426. The rod 414 has a threaded portion 428 that permits the location of the spring cap 426 to be adjusted so that a preload can be applied to the springs 424, 426. The housing 418 includes a rocker arm mounting portion 430. The stabilizer member assembly 410 tops-out or bottoms-out when either of the springs 422, 424 are fully compressed. In one embodiment, the alternate stabilizer member assembly 410 is substituted for one of the stabilizer member assemblies 84 a, 84 b, and a rigid rod is substituted for the other stabilizer members assembly.

[0053] FIGS. 5-7 illustrate various views of the stabilizer assembly 74 with the primary support structure 22 removed. In a horizontal resting state, the shock absorbers/spring assemblies 70 a, 70 b (see FIG. 8) provide a downwardly biasing force 140 a, 140 b on the spindle housings 36 a, 36 b. The horizontal resting state refers to the snowmobile being stationary on a substantially horizontal surface. When an upward bump force 144 greater than the force 140 a is imposed on the spindle housing 36 a, the lower control arm 32 a will rotate in a direction 146 a around the lower control arm axis 34 a. Rotation of the lower control arm 32 a displaces the stabilizer bracket 88 a in a direction 148. Assuming that the stabilizer member assembly 84 b is at its fully elongated or topped-out position, displacement of the stabilizer bracket 88 a in the direction 148 will have the effect of rotating the rocker arm 76 in the direction 142, which in turn will move the stabilizer member assembly 84 b in a direction 150.

[0054] Once the stabilizer member assembly 84 b is in the fully elongated position, movement of the stabilizer bracket 88 b in the direction 150 will have the effect of raising the lower control arm 32 b in opposition to the force 140 b provided by the shock absorber 70 b. Consequently, spring force from the shock absorber 70 b will be transferred to the lower control arm 32 a on the other side of the modular front suspension system 20.

[0055] In another embodiment, preload adjustment screws 128 a, 128 b are advanced so that the sleeves 98 a, 98 b partially compress the springs 122 a, 122 b. When in the horizontal resting state, any load on the springs 122 a, 122 b will cause the stabilizer member assemblies 84 a, 84 b to elongate to their maximum length and rotate the rocker arm 76 in a direction 142. Ultimately, the stabilizer member assemblies 84 a, 84 b are in their fully extended state and do not rotate the rocker arm 76 any further. At this point, further advancing the sleeves 98 a, 98 b using the preload adjustment screws 128 a, 128 b will develop a preload in the springs 122 a, 122 b.

[0056] When the bump force 144 increases to a level that is greater than the shock absorber/spring assembly force 140 a, the lower control arm 32 a rotates in a direction 146 a. Rotation in the direction 146 a is initially resisted by a combination of the downward force 140 b on the spindle housing 36 b, as discuss above, and the spring force from spring 122 a. As the spring 122 a is compressed, the spring force of spring 122 a rises until it overcomes the downward force 140 b from the shock absorber/spring assembly 70 b, forcing the lower control arm 32 b to rotate in the direction 146 b. As the lower control arm 32 b rotates in the direction 146 b, the shock absorber/spring assembly 70 b is compressed and the force 140 b increases. A component of the increased force 140 b is transmitted through the stabilizer assembly 74 to the spindle housing 36 a.

[0057] The configuration discussed above allows for a non-linear relationship between the stabilizer mechanism 74 and the shock absorber/spring assemblies 70 a, 70 b. For example, it is possible to have a firm initial roll stiffness of the snowmobile for smooth comers and soft roll stiffness for bumpy corners by increasing the preload on the springs 122 a, 122 b. Alternatively, for a more linear relationship between the stabilizer mechanism 74 and the shock absorber/spring assemblies 70 a, 70 b, less preload on the springs 122 a, 122 b is used.

[0058] One practical application of the present stabilizer assembly 74 is that is provides initially very stiff displacement of the lower control arms 32 a, 32 b for smooth cornering on relatively smooth surfaces. When rough terrain is encountered, further displacement of the lower control arms 32 a, 32 b will require less additional force than the original displacement. In one embodiment, the force-displacement curve for the present stabilizer assembly 74 is essentially a step function in which the force per unit displacement is reduced after an initial amount of displacement is achieved.

[0059]FIGS. 8 and 9 illustrate a modular front suspension system 20 in accordance with the present invention mounted to a snowmobile frame 200. The primary support structure 22 is attached to upper frame members 202 a, 202 b at upper frame mounting locations 204 a, 204 b. Lower frame members 206 a, 206 b are attached to the primary support structure 22 at lower frame mounting locations 208 a, 208 b. Removable fasteners, such as bolt, are preferred for attaching the primary support structure 22 to the snowmobile frame 200. The primary support structure 22 permits easy assembly and removal of the modular front suspension system 20 from the snowmobile frame 200. Additionally, the primary support structure 22 provides a substantial barrier that protects motor compartment 210.

[0060] The snowmobile frame 200 includes a left frame portion 220 a and a right frame portion 220 b. The left and right frame portions 220 a, 220 b are join together by an upper cross piece 224 and a lower cross piece 226 immediately behind the engine compartment 210. Vertical supports 209 a, 209 b extends between frame members 202 a, 206 a and 202 b, 206 b, respectively. The lower frame members 206 a, 206 b extend rearward of the engine compartment 210. Upper rear frame member 228 a extends from the upper portion of the vertical support 209 a to the distal rearward end of the lower frame member 206 a. The frame members 228 a and 206 a are joined at a mounting plate 232 a. Upper rear frame member 228 b extends from about the upper portion of the vertical support 209 b to the distal rearward end of the lower frame member 206 b. The frame members 228 b and 206 b are joined at a mounting plate 232 b. The rearward frame members 228 a, 206 a are not connected to the rearward frame members 228 b, 206 b at any location behind the vertical supports 209 a, 209 b and the cross pieces 224, 226, thereby reducing the weight of the frame 200. The independent, free-floating nature of the rearward frame members 228 a, 206 a and 228 b, 206 b is believed to improve the handling properties of the snowmobile.

[0061]FIG. 9 is a side view of the snowmobile chassis 240 including a protective shell 214 attached to, and extends between, the rearward frame members 228 a, 206 a and 228 b, 206 b. The protective shell 214 prevents snow and debris from reaching seat region 402. In the illustrated embodiment, the protective shell 214 is constructed from a resin-based material, such as fiberglass or fiberglass reinforced with Kevlar® fibers or other lightweight reinforcing materials. Kevlar is an aromatic polyamid fiber of extremely high tensile strength and greater resistance to elongation than steel. It has high-energy absorption properties that make it particularly suitable for use as a reinforcing material for plastic composites.

[0062] The protective shell 214 is typically not a structural member for transferring loads between the rearward frame members 228 a, 206 a and 228 b, 206 b. Loads are transferred between these rearward frame members by the rear suspensions system for the endless track, such as the suspension systems disclosed in U.S. Pat. Nos. 5,370,198 and 5,667,031, and U.S. patent application Ser. No. 08/853,442 entitled Vehicle Suspension System with Variable Geometry, filed May 9, 1997.

[0063] The primary support structure 22 with the front suspension components removed is shown mounted to the snowmobile chassis 240. Center opening 72 is typically perpendicular to the longitudinal axis of the snowmobile frame 200. Steering brackets 24 are located behind the primary support structure 22 in the motor compartment 210 to protect them from damage during impacts with obstacles. Additionally, heat generated within the motor compartment 210 may reduce the accumulation of ice and snow on the steering linkage mechanism (not shown).

[0064]FIGS. 10, 11, and 12 are various perspective views of a snowmobile chassis 240 of the present invention. The protective shell 214 has a center portion 251 and left and right side portions 250, 252 extending downward towards the upper rear frame members 228 a, 228 b, respectively. The protective shell 214 can flex at the intersection of the side portions 250, 252 and the center portion 251 during snowmobile operation. Running boards 254, 256 extend laterally outward from the side portions 250, 252, respectively.

[0065] As best seen in FIG. 12, the protective shell 214 defines a top edge of an endless belt channel 260 extending along the rear portion of the chassis 240 between the rear frame members 206 a, 228 a and 206 b, 228 b. Drive shaft 262 extends across the width of the endless belt channel 260 for engagement with the endless belt (see FIG. 14). In the illustrated embodiment, one end of the drive shaft 260 is directly mechanically coupled to a gearbox 264. The gearbox 264 has a driven pulley input opening 266 for receiving a driven pulley 286 (see FIG. 14). A rotor 270 and a caliber 272 are located on the other end of the drive shaft 262 for providing a breaking force. The rotor 270 and caliber 272 operate as a conventional disk brake system.

[0066]FIGS. 13 and 14 illustrate a side and top view of a snowmobile chassis 240 and drive train in accordance with the present invention. Motor 280 is retained in the motor compartment 210 by various motor mounts 282, 284. In the illustrated embodiment, motor mounts 282 are rigidly connected to the primary support structure 22. In the illustrated embodiment, the motor 280 is a 700 cc twin cylinder, liquid cooled engine generating about 120-125 HP at 8150 RPM, with 83 foot pounds of torque at 8000 RPM, available from Polaris Industries., Inc. of Roseau, Minn. The motor 280 is arranged with carburetors 287 located towards the front, immediately behind the primary support structure 22. Exhaust ports 288 are located on opposite sides of the motor 280.

[0067] As is often the case, the exhaust ports 288 are located higher on the motor 280 than the carburetor 287. By arranging the motor 280 with the exhaust ports 288 towards the rear, there is more room to lower the motor 280 further into the chassis 240, resulting in a lower center of gravity for the snowmobile 400. In the embodiment illustrated in FIG. 13, the locations of the carburetors 287 and exhaust ports 288 generally follow the contour or slope of the upper frame members 202 a, 202 b. It is estimated that the motor 280 is located about 5.1 centimeters to about 7.6 centimeters (2 to 3 inches) lower in the chassis 240 than on comparably powered snowmobiles.

[0068] The carburetors 287 tend to require more space than the exhaust system 290. Consequently, locating the carburetors 287 in the front allows the motor 280 to be located closer to the rear of the motor compartment 210. Locating the exhaust system 290 between the motor 280 and the steering column 292 contributes to mass centralization, a lowering the center of gravity and reducing the overall length of the snowmobile, thereby increasing handling performance and ride quality. Additionally, locating the carburetors 287 on the front of the motor 280 is believed to reduce the occurrences of vapor lock. Finally, when the snowmobile is parked in a slightly downhill configuration, fuel will drain from the motor 280 towards the carburetor 287, reducing the chance of engine flooding.

[0069] Drive clutch 300 is coupled directly to the crankshaft 302 of the motor 280. The drive clutch 300 is mechanically coupled to the driven pulley 286 by a continuous belt 304. As discussed above, the driven pulley 286 is directly mechanically coupled to the gear box 264. Power is transmitted through a matched set of gears, thereby eliminating the intermediate chain drive that typically is located between the drive pulley and the drive shaft. This partial direct drive configuration increases reliability of power transmission to the track or belt. The drive shaft 262 includes a series of drive wheels 340 having appropriately spaced teeth 342 that engage with ridges on the endless track or belt. A suitable endless track or belt is available from Camoplast Thermoplastic Group of Sherbrooke, Quebec.

[0070] An oil tank 350 is located under the steering column 292. A fuel tank 352 is located on the protected shell 214 behind the fuel tank 352. A steering column support structure 354 extends over the fuel tank 352 and supports the steering column 292. A flap 356 is mounted on the end of the protective shell 214 to reduce the snow and debris thrown by the endless track.

[0071] As best seen in FIG. 14, a torque arm 310 extends between a bracket 312 rigidly attached to the frame 200 and the driven pulley 268. The torque arm 310 provides a counteracting force 314 that opposes the force 316 generated by the drive belt 304. A quick release pin 318 is provided on the torque arm 310 to permit the drive belt 304 to be easily replaced as needed. As best illustrated in FIG. 15, the torque arm 310 includes a bearing 320 that engages with a distal end of the driven pulley 268.

[0072]FIG. 16 is an exploded view of the gear box 264 in accordance with the present invention. Since the motor 280 is mounted with the crank shaft 302 facing to the right, the drive clutch 300 is turned in the opposite direction of rotation than on a conventional snowmobile. The gear box 264 reverses the direction of the drive system rotation for delivery to the drive shaft 262 and provides the final ratio reduction for the drive train. The driven pulley 286 is directly coupled to a first gear 330 through the opening 266. The gear 330 preferably includes bearings 332 to minimize internal friction and wear. The first gear 330 is meshed with second gear 334, which reverses the direction of rotation of the drive system. The drive shaft 262 is directly coupled to the second gear 334 through the opening 336. In the illustrated embodiment, the gears 330, 334 are covered in a housing 338 with appropriate mounting holes for attachment to the vehicle chassis 240.

[0073] The complete disclosures of all patents, patent applications, and publications are incorporated herein by reference as if individually incorporated. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein. 

What is claimed is:
 1. A modular front suspension system for a snowmobile having a chassis with a powered endless belt drive system and a pair of forwardly mounted steerable skis attached to the chassis by the modular front suspension system, the modular front suspension system comprising: a primary support structure having first and second ends, a center opening and at least one mounting surface attachable to the chassis; a pair of upper control arms pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively: a pair of lower control arms pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively; a pair of ski spindle housings pivotally connected to distal ends of the upper and lower control arms, respectively, the ski spindle housings being connectable to the steerable skis, and a stabilizer assembly mechanically coupling the ski spindle housings.
 2. The system of claim 1 wherein the stabilizer assembly extends through the center opening.
 3. The system of claim 1 further comprising: a pair of shock mounts pivotally attached to one of the upper control arm, primary support structure or the vehicle chassis; and a pair of shock absorber attached to the shock mounts and the spindle housings, respectively.
 4. The system of claim 3 further comprising a link pivotally connecting the shock mounts and the respective lower control arms.
 5. The system of claim 1 further comprising: a pair of shock mounts pivotally attached to the primary support structure; a link connecting the pair of shock mounts to the respective lower control arms; and a pair of shock absorber connected to the shock mounts and the spindle housings, respectively.
 6. The system of claim 1 wherein the primary support structure further comprises steering brackets for receiving a steering linkage connectable to the steerable skis.
 7. The system of claim 1 wherein the primary support structure further comprises motor mounting locations.
 8. The system of claim 1 wherein the stabilizer assembly is connected to one of the lower control arms, the upper control arms, the shock mounts or the lower shock mounts.
 9. The system of claim 1 wherein the stabilizer assembly comprises: first and second stabilizer brackets attached to the lower control arms respectively; a rocker arm having first and second ends pivotally mounted on the primary support structure; a first stabilizer member assembly pivotally connected to the first stabilizer bracket and the first end of the rocker arm; and a second stabilizer member assembly pivotally connected to the second stabilizer bracket and the second end of the rocker arm.
 10. The system of claim 9 wherein the first stabilizer member assembly comprises: an extendable rod assembly having a maximum extension and a spring cap fixed thereto; a sleeve slidably engaged with the extendable rod assembly adjacent to the first stabilizer bracket; and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve.
 11. The system of claim 10 further comprising an adjustment mechanism or sliding the sleeve along the extendable rod assembly to apply a bias of the spring when the extendable rod as at the maximum extension.
 12. The system of claim 10 wherein the extendable rod assembly comprises a telescoping structure.
 13. The system of claim 9 wherein the second stabilizer member assembly comprises: an extendable rod assembly having a maximum extension and a spring cap fixed thereto; a sleeve slidably engaged with the extendable rod assembly adjacent to the second stabilizer bracket: and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve.
 14. The system of claim 13 wherein the first and second stabilizer member assemblies are in a fully extended configuration when the snowmobile is in a substantially horizontal resting state.
 15. The system of claim 9 wherein the first stabilizer member assembly comprises a double-acting spring assembly and the second stabilizer members assembly comprises a rigid shaft.
 16. The system of claim 9 wherein the rocker arm is located in the center opening of the primary support structure.
 17. The system of claim 1 wherein the primary support structure comprises one of an extrusion, a casting, a welded structure or a formed structure.
 18. The system of claim 1 wherein the respective upper control arm axes are located above the lower control arm axes when the primary support structure is attached to the chassis.
 19. A modular front suspension system for a snowmobile having a chassis with a powered endless belt drive system and a pair of forwardly mounted steerable skis attached to the chassis by the modular front suspension system, the modular front suspension system comprising: a primary support structure comprising a hollow member having first and second ends, a center opening and at least one mounting surface attachable to the chassis; a pair of upper control arms pivotally connected to the first and second ends of the primary support structure at upper control arm axes, respectively; a pair of lower control arms pivotally connected to the first and second ends of the primary support structure at lower control arm axes, respectively; a pair of ski spindle housings pivotally connected to distal ends of the upper and lower control arms, respectively, the ski spindle housings being connectable to the steerable skis: a pair of shock mounts pivotally attached to one of the upper control arm or primary support structure, respectively; and a pair of shock absorber attached to the shock mounts and the spindle housings, respectively.
 20. A stabilizer assembly for a front suspension system of a snowmobile, the front suspension system having a pair of control arms pivotally connected to the snowmobile, a pair of skis pivotally connected to distal ends of the control arms, and biasing members biasing the pair of control arms downward relative to the snowmobile, the stabilizer assembly comprising: first and second stabilizer brackets attached to the control arms, respectively; a rocker arm having first and second ends pivotally mounted to the snowmobile; a first stabilizer member assembly pivotally connected to the first stabilizer bracket and the first end of the rocker arm; and a second stabilizer member assembly pivotally connected to the second stabilizer bracket and the second end of the rocker arm.
 21. The assembly of claim 20 wherein the first stabilizer member assembly comprises: an extendable rod assembly having a maximum extension and a spring cap fixed thereto; a sleeve slidably engaged with the extendable rod assembly adjacent to the first stabilizer bracket; and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve.
 22. The assembly of claim 21 further comprising an adjustment mechanism for sliding the sleeve along the extendable rod assembly to apply a bias of the spring when the extendable rod is as the maximum extension.
 23. The assembly of claim 21 wherein the extendable rod assembly comprises a telescoping structure.
 24. The assembly of claim 20 wherein the second stabilizer member assembly comprises: an extendable rod assembly having a maximum extension and a spring cap fixed thereto; a sleeve slidably engaged with the extendable rod assembly adjacent to the second stabilizer bracket; and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve.
 25. The assembly of claim 20 wherein the first and second stabilizer member assemblies are in a fully extended configuration in a substantially horizontal resting state.
 26. A stabilizer assembly for a front suspension system of a vehicle, the front suspension system having a pair of control arms pivotally connected to the vehicle, a pair of wheels pivotally connected to distal ends of the control arms, and biasing members biasing the pair of control arms downward relative to the vehicle, the stabilizer assembly comprising: first and second stabilizer brackets attached to the control arms, respectively; a rocker arm having first and second ends pivotally mounted to the vehicle; a first stabilizer member assembly pivotally connected to the first stabilizer bracket and the first end of the rocker arm; and a second stabilizer member assembly pivotally connected to the second stabilizer bracket and the second end of the rocker arm.
 27. A stabilizer assembly for a front suspension system of a snowmobile, the front suspension system having a pair of control arms pivotally connected to the snowmobile, a pair of skis pivotally connected to distal ends of the control arms, and biasing members biasing the pair of control arms downward relative to the snowmobile, the stabilizer assembly comprising: first and second stabilizer brackets attached to the control arms, respectively: a rocker arm having first and second ends pivotally mounted to the snowmobile; a first stabilizer member assembly pivotally connected to the first stabilizer bracket and the first end of the rocker arm, the first stabilizer member assembly comprising an extendable rod assembly having a maximum extension and a spring cap fixed thereto, a sleeve slidably engaged with the extendable rod assembly adjacent to the first stabilizer bracket, and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve; and a second stabilizer member assembly pivotally connected to the second stabilizer bracket and the second end of the rocker arm; the second stabilizer member assembly comprising an extendable rod assembly having a maximum extension and a spring cap fixed thereto, a sleeve slidably engaged with the extendable rod assembly adjacent to the second stabilizer bracket, and a spring arranged around the extendable rod assembly and interposed between the spring cap and the sleeve.
 28. The assembly of claim 27 wherein the first and second stabilizer member assemblies are in a fully extended configuration in a substantially horizontal resting state.
 29. The assembly of claim 27 wherein springs of the first and second stabilizer member assemblies comprise a preload in the horizontal resting state.
 30. The assembly of claim 25 wherein initial upward displacement of one of the skis is resisted by a first force, and subsequent upward displacement of that ski is resisted by a second force proportionally less than the first force.
 31. The assembly of claim 25 wherein initial upward displacement of one of the skis is resisted by a first force, and subsequent upward displacement of that ski is resisted by a second force proportional to the first force.
 32. A chassis for a snowmobile having an endless belt drive system, the chassis comprising: a plurality of front structural members defining a motor compartment: front suspension system mounting locations on distal ends of two or more of the front structural members; a pair of independent, rear structural members rigidly connected to the front structural members and extending rearwardly from the motor compartment on opposite sides of an endless belt channel; and a protective shell extending between the pair of rear structural members and over the endless belt channel, the protective shell comprising a light-weight, resin based material transferring substantially no loads between the pair of rear structural members.
 33. The snowmobile chassis of claim 32 further comprising a rear suspension system extending between the pair of rear structural members, the rear suspension system transferring substantially all loads between the pair of rear structural members.
 34. The snowmobile chassis of claim 33 further comprising a motor located in the motor compartment, the motor having at least one carburetor positioned on a first side of the motor adjacent to the front suspension system mounting locations and at least one exhaust port positioned on an opposite side of the motor and generally in the direction of the rear structural members.
 35. A snowmobile assembly having an endless belt drive system comprising: a snowmobile chassis having a motor compartment at a front portion and an endless belt channel at a rear portion; a motor located in the motor compartment, the motor having at least one exhaust port positioned toward the rear portion of the snowmobile chassis; a drive clutch on the motor; a driven pulley on the gear box located adjacent to the endless belt channel, an endless belt drive shaft located in the endless belt channel and mechanically coupled directly to the gear box; a drive belt mechanically coupling the drive clutch to the driven pulley; and a torque arm connecting the driven pulley to the snowmobile chassis.
 36. The snowmobile of claim 35 wherein the gear box comprises two or more gears directly coupling the driven pulley to the endless belt drive shaft. 